Abundances in Spiral Galaxies: Evidence for Primary Nitrogen Production
van Zee, L., Salzer, J.J., & Haynes, M.P. 1998, ApJL, 497, L1
Abstract
We present the results of nitrogen and oxygen abundance measurements
for 185 HII regions spanning a range of radius
in 13 spiral galaxies. As expected, the
nitrogen-to-oxygen ratio increases linearly with the oxygen abundance for
high metallicity HII regions, indicating that nitrogen is predominately
a secondary element. However, the nitrogen-to-oxygen ratio plateaus for oxygen
abundances less than 1/3 solar, as is also seen in
low metallicity dwarf galaxies. This result suggests that the observed trend in
dwarf galaxies is not due to outflow of enriched material in a shallow
gravitational potential. While the effects of
infall of pristine material and delayed nitrogen delivery are
still unconstrained, nitrogen does appear to have both a primary
and secondary component at low metallicities in all types of galaxies.
ADS abstract
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